The area of a parallelogram is determined by multiplying the base, b, with the height,

h, of the parallelogram:

A = b • h

The area of a triangle is determined by multiplying the base, b, with the height, h, of the triangle and divide by two:

A = b • h/2

The area of a trapezoid is determined by multiplying the mean value of the two bases, b1 and b2, with the height, h, of the trapezoid:

A = h • b1 + b2 /2

The area of a rhombus is determined by half the product of the two diagonals:

A = ½(AC)(BD)

The area of a regular polygon is determined by the product of the perimeter, P, and what is called an apothem, a (see figure below):

A = Pa/2

The area of a circle is determined by multiplying the square of the radius, r, with the constant pi:

A = πr2

Video lesson: Find the area of the triangle.

To see the solution look at the video in the next page.

Here we have a triangle and what we’re give is this height; 5, and this base; 6. We can find the area of this triangle from the definition which is one half base times height and those are exactly the pieces of information that we’re given. So we can just plug those in and solve for the area. So the area is one half the base which is 6 times the height which is 5. So we can say the area is one half of 6 which is 3 times 5. Finally if I can do 3 times 5 in my head which is 15 we can say that the area of this triangle is 15 square units.